Electromagnetic methods of torquing gyroscopes include variable reluctance torquers and rotating polarized magnets placed in the field of a solenoid which is energized at various times during a single revolution of the gyroscope magnet assembly. One disadvantage of present electromagnetic torquers especially as applied in spherical gas gyroscopes used for optical terminal guidance is that they require a very large magnetic return path as part of the gyro rotor. Magnetic materials exhibit high density and the requirement of a large return path increases the mass and inertia of the gas suspended gyro rotor. Also present design requires the return path to be a two piece assembly of the magnetic upper and lower hemispheres. This results in losses due to the magnetomotive force required to overcome the reluctance of the joint.
Another disadvantage of prior art electromagnetic torquers is that in gyro optical systems there is a requirement that the optical element or assembly be made part of the gyroscopic element. An optical aperture, as large as possible, is desired on such systems. These optics are placed on the spin axis and protrude from the spherical rotor. In variable reluctance torquers taught by the prior art, the angular freedom of the rotor was severly constrained by the wrap around torquers, which would collide with the optical assembly. See for example, the gyro optical device disclosed in U.S. Pat. No. 3,920,200. The present invention satisfies the need for increased angular freedom and increased apertures.